1. Field of the Invention
The disclosed embodiments of the present invention relate to switch control circuits of a bridgeless switching circuit and a power converter and related method thereof, and more particularly, to a control circuit for controlling a conducting status of a first switch element and a second switch element within a bridgeless switching circuit and related method thereof.
2. Description of the Prior Art
To enhance the power conversion efficiency, the number of switches and the voltage drop loss of the switches are deceased as much as possible in the conventional alternating current-direct current power converter (AC-DC power converter). For example, by employing a bridgeless switching circuit which collaborates with a related power factor correction circuit, it may decrease the number and the voltage drop of the switches in the conduction path and thereby enhance the power conversion efficiency. Please refer to FIG. 1, which is a diagram illustrating a conventional bridge power converter 1000 employed to convert an alternating current of an AC power SA to generate a direct current to a load Rload. The bridge power converter 1000 includes a plurality of diodes D1-D4, a plurality of capacitors C1 and C2, an inductor L1, and a switch element SW1 (implemented by a metal-oxide-semiconductor field effect transistor (MOSFET)) and a diode DA both used for rectification. As a person skilled in the art can readily understand operations and details of the circuit shown in FIG. 1, further description is omitted here for brevity. However, in the conversion process of the bridge power converter 1000 shown in FIG. 1, the switch element SW1 may perform rectification on the AC power SA according to an input signal S1, and a current conduction path within the bridge power converter 1000 may pass through three diodes (i.e., diodes D1, DA, and D4 in order, or diodes D2, DA, and D4 in order). That is, the converted voltage has to overcome three voltage drops of the three diodes to charge the load Rload successfully.
Please refer to FIG. 2, which is a diagram illustrating a conventional bridgeless power converter 2000 employed to convert an alternating current of an AC power SA to generate a direct current to a load Rload. The bridgeless power converter 2000 includes a plurality of inductors L1 and L2, a plurality of diodes D1 and D2, a plurality of switch elements SW1 and SW2 each implemented by a metal-oxide-semiconductor field effect transistor (MOSFET), and a capacitor C1, wherein when the switch elements SW1 and SW2 are not switched on, they may bear the characteristics of body diodes (i.e., diodes D3 and D4 shown in FIG. 2), respectively. In other words, switch elements SW1 and SW2 may respectively bear characteristics of switches and characteristics of diodes D3 and D4 used for half rectification according to phases of the inputs S1 and S2. Compared to the bridge power converter 1000, the bridgeless power converter 2000 has a conduction path having only two voltage drops of switch elements (e.g., voltage drops of the diode D1 and the body diode D4 in the switch element SW2, or voltage drops of the diode D2 and the body diode D3 in the switch element SW1). Therefore, the bridgeless power converter 2000 may further enhance the power conversion efficiency.
However, as for the conventional bridgeless power converter 2000, the input signals received by the switch elements SW1 and SW2 may have the same waveform. That is, both of the switch elements SW1 and SW2 are either switched on or switched off at the same time due to the input signals S1 and S2 with the same waveform. In addition, the frequent switching of the switch elements SW1 and SW2 may result in unnecessary power loss. Thus, how to improve the switch control method of the bridgeless switching circuit and enhance the power conversion efficiency is a serious issue in the pertinent field.